The primary goal of the experiments proposed in this application is to identify dimensions of SI cortical neuroelectrical activity that could account (i.e., serve as the SI correlate) for the perceptual experiences evoked by selected conditions of single- and multi-site skin stimulation. Every experiment will obtain measures of both the global and single neuron responses to each stimulus condition by using a novel and powerful combination of the methods of near-infrared optical intrinsic signal (OIS) imaging and extracellular recording of single neuron spike discharge activity. Two series of combined OIS imaging/neurophysiological recording experiments are proposed. In the first series (Series I), the global and single neuron responses evoked by single-site skin stimulation will be obtained for skin flutter stimuli that differ only in amplitude. Each experiment of this series will use the same range of amplitudes used in published human psychophysical studies of the effects of flutter amplitude on perceived intensity. The Series II experiments will evaluate the responses of SI to dual-site skin flutter stimulation - they will seek to identify SI correlates for well-established perceptual phenomena (e.g., spatial compression, intensity modulation, etc.) that human psychophysical studies have demonstrated under comparable conditions of multi-site skin stimulation. Collectively, the information obtained in the Series I and II experiments should enable quantification of stimulus-directed interactions between topographically and cytoarchitectonically distinct regions within SI cortex - interactions of considerable potential functional importance which although predicted on theoretical grounds, have not been addressed in any experimental study published to date. [unreadable] [unreadable]